After some time first automatic link exchange systems appeared. They’re based on simple algorithm: you register in this system, install special code on your web site which will display links to other sites of this system.

First automatic link exchange systems were very weak and easily detectable by SE.

Sometime later automatic link exchange systems find way to mask that site participates in link exchange by hiding any mentonion about link exchange. Example of such system is TelaLinks

Alternative way of link exchange is automatic link trade systems which appeared last time. This systems are more gentl. It allows easy link trade between site owners and optimizers. Everybody registers in system and makes his sites availale by search from other side. Link trade system automatically performs and controls link purchases and sales. For example if link is disappeared for some reason then optimizer will be notified about this. These systems also performs centralized billing for all operations.  Example of such system: E-Links

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